Impregnated paper product



Patented Jan. 30, 1934 ILUNITED STATES PATENT OFFICE mrnnona'rnn PAPERrnonuc'r poration of Delaware No Drawing. Application April 1, 1933 ISerial No. 664,043

19 Claims.

This invention relates to impregnated sheet material and moreparticularly to an impregnated cellulose fabric which exhibits toan-exceptional degree those properties most desired in artificialleather products.

This case is a continuation in part of application Serial No. 599,808filed March 18, 1932, which is a continuation in part of Patent No.1,857,100.

Among the various methods suggested for making absorbent paper andimpregnated products therefrom is one which consists of manufacturing apuffed paper by immersing a sheet of paper in strong caustic solution'and'drying the sat- 16 urated sheet in air. The absorption of carbondioxide causes the formation of sodium carbonate crystals which aresubsequently washed out. The pufling efl'ect is due to the formation ofthe cystals in the sheet. The long contact of 20 the fibers with thestrong caustic prevents any appreciable crinkling of the fibers.Furthermore, the restricted movement of the fibers when treated in sheetform prevents the formation of a base having the high degreeof crinkle,high freeness and capability of uniform impregnation which characterizesthe product of the present invention. Prior treatments of paper pulpwith caustic have been chiefly concerned with the manufacture of highalpha cellulose through solution of the non-alpha celluloses by thecaustic. The solution of the non-alpha cellulose bonding materials,which is the object of the process, causes the original fiber toseparate into the finer component fibers. The fibers are also shortenedbecause the end portions, which are thinner than the middle portions,are dissolved off. This shortening and thinning of the fiber isevidenced by the slowness of the treated pulp and the decrease in thefreeness value from that of the original pulp. High alpha cellulosepapers now known are too expensive for general use as an impregnatingbase and the impregnated products possess certain deficiencies.

This invention has as an object an improved method of making artificialleather and 'sheet impregnated products in general. A further object isnew and improved impregnated material products having-a base of feltedpaper making fibers. Other objects will appear hereinafter.

These objects are accomplished by preparing a fabric base in the specialmanner disclosed in the patent mentioned above and impregnating it withcertain colloidal impregnating materials as will more fully appear inthe following specification.

(c1. s2-4o) The fabric base is a paper or felt made of artificiallycrinkled cellulose fibers having a high freeness. The'method of makingthe base, as disclosed in the mentioned cases, is briefly as follows:Paper pulp is treated with a solution of 80 caustic soda of mercerizingactivity under conditions which cause only a superficial reactionbetween the pulp and the caustic. To this end the reaction is stoppedshort of gelatinizatlon, and the mercerizing action of the caustic isnot allowed to proceed appreciably beyond a superficial or skin eifect.The method of treating the pulp to bring about these conditions consistsin dispersing the pulp with the caustic at high pulp consistencies (alow ratio of liquor to pulp) and diluting the caustic below mercerizingactivity promptly after the fibers have been dispersed from the pulpmass and wet with the solution. By high pulp consistencies we meanconsistencies above 10%,i. e., more than 10 parts by weight 7 of pulpper 90 parts by weight of liquor. For most purposes, however, we preferto use consistencies from 15 to 20%. The maximum usable consistencycorresponds to the minimum volume of liquor that will thoroughly wet thefibers in a time short enough so that the concentration of the liquor isnot materially lowered by reaction with the fibers before all of thefibers are wet. Simultaneously with the wetting of the fibers by themercerizing solution the crinkle and freeness of the pulp is at amaximum and these values decrease with increasing time of treatment. Theuse of high pulp consistencies has the efiect of retarding the timeaction of the caustic on the fibers. Even with these high pulpconsistencies, however, the solution should, for the best results, beremoved promptly, a time as long as thirty minutes being usuallyundesirable except for certain highly resistant pulp such as rope. Whenusing mechanism specially designed for swift dispersion of the fibersand prompt dilution of the caustic in contact therewith, it is not,except for economic reasons. essential that a low ratio of liquor topulp be used.

The initial material is preferably kraft paper pulp. Unlike the processfor treating pulp to make high alpha cellulose, the action of thecaustic in the present process is stopped before a major portion ofnon-alpha cellulose constituents are removed from the fibers and beforethe ultimate fibers have been liberated by solution of the ligneousbonding materials and the non-alpha. cellulose constituents.

Various other reagents may be used instead of caustic soda. Thesereagents are those which at 0 iii? suitable concentration andtemperature are capable dissolving or dispersing cellulose, theconcentra ion of the reagent being within the range known as mercerizingstrength, that is the concentration commonly used in mercerizing cottongoods. For a given concentration of these reagents the mercerizingactivity of the solution is dependent upon the temperature. In the caseof caustic soda, which is our preferred reagent, the activity increasesas the temperature is lowered.

Inasmuch as the strength of a particular solution required to show amercerizing effect may vary somewhat depending upon whether the fiber ismore or less resistant than cotton fibers, we desire it to be understoodthat by solutions of mercerizing activity we mean solutions of suchstrengths which will produce the characteristic effects of mercerizationin the particular fiber treated. The caustic content of a solution thatmay be designated as being of mercerizing activity at any giventemperature is well understood by those skilled in the fiber art. Acaustic solution of this strength improves the luster oi fabric and alsoimproves the dyeing properties and tensile strength. The dye absorbencyof the fibers of paper pulp is also increased, the X-ray patternchanged, the ease of the hydration reduced, and the fiber changed from afiat ribbon form to a rod-like form.

The concentration of solution required to give the necessary mercerizingactivity may, for practically all purposes, be defined as a solutionhaving a mercerizing activity equivalent to that of an aqueous sodiumhydroxide solution of 8% to concentration at 25 0.

While the process may be operated between the freezing point of thecaustic solution and the temperature at which degradation of the fibersbegin (from i0 C. to about +104 0'. for sodium hydroxide) it is notdesirable to operate at the lower and the higher temperatures becausethe gelatinizing action at the lower temperatures and the degradingaction at the higher temperatures takes place with such rapidity that itis difficult-to effect distribution of the caustic throughout the pulpand to wash out the caustic to stop the reaction in time required toprevent the mentioned gelatinizing and degrading action from decreasingthe amount of crinkle in the fibers below the desired value. It ispreferred, therefore, to operate at temperatures not far removed fromroom temperatures. The best commercial operating conditions are between20 C. and C. with a concentration above 10%. We prefer to use an 18%concentration at room temperature.

The fibers must be in pulp form during the caustic treatment, and bypulp it is to be understood that we mean-cellulosic fibrous materialconsisting of fibers not arranged into sheets and short enough andsufiiciently low in diameter to he made into a uniform felt from a watersuspension. The fibers must be of paper-making length, and long fibers,such as those separated from the raw materials by some form of degummingprocess, will not give the kind of product with which the presentinvention is concerned. Fibers that may be designated as paper makinglength have a minimum mean length of about mm. and a maximum mean lengthof about d mm. Because of the fact that fibers having a mean length ofless than 1 mm, such as the fibers of non-coniferous wood pulp, do notcrinkle as intensely as the longer fibers within the paper= makingrange, we prefer, especially when wag-lg ing with the weaker solutionswithin the mercerizing range to use fibers having a mean length of 1%;to e In preparing the pulp for the paper base the non-fluid highconsistency mixture of pulp and caustic solution may be dispersed intothe free fibers by means of the ordinary Hollander heater having thebeater roll raised from the bed plate so that the pulp is squeezedwithout abrasive action. The pulp may be forced under the roll withpaddles. After substantially all of the fibers have been separated fromthe mass and individually wetted with the caustic, a stream of water isrun into the heater in order to stop the reaction.

For dispersing the pulp with the caustic, we prefer, however, to use aswifter dispersing mechanism such as the disc refiner described andillus= trated in detail in our mentioned patent.

The following examples in which the parts are by weight, areillustrative of the method for carrying out the invention:

Example I Kraft pulp, 90% bone dry (freeness on special tester seconds)1000 lbs. Sodium hydroxide (aqueous solution 18.5% at 21 C.) @000 lbs.

The pulp was passed into the disc refiner with a fixed rate of feedingthe solution and pulp so as to give a uniform consistency. The strengthof the solution in contact with the fibers during the treatment was 18%and the time of treatment with this solution was 3.5 seconds. Thefreeness after completing the treatment was 21.2 seconds. The treatedpulp gave a dark blue color with zinc chloriodine reagent. '1

A sheet of felt was formed from this pulp by the following process: Thepulp was dispersed in Hollander heaters with the rolls in a lightbrushing position for a half hour to disperse the fibers. The pulp wasthen let down into a preparation chest and after the pulp was dilutedwith some water and stirred just enough to keep it in suspension it waspumped through a Jordan in which the cone was backed oi? the bars toprevent cutting. Following dilution with more water in a machine chestthe pulp was pumped to a flow box above plate screens where it wasdiluted to a consistency of 0.4%, screened and passed onto a Fourdrinierprovided with three slices and having an up-hill pitch of one inch forsix feet of length. The shake was thirty per minute at an amplitude ofthree eighths inch. The first press roll was felt covered. After dryingon regular papermachine driers the sheet was passed between two calendarrolls to soften. The final sheet was .060 inches thick and weighed. 0.68pounds for an area of 36x40 inches.

The felt thus produced was impregnated with a composition consisting of:

, Parts Asphalt (M. P. 170 C.) 100 Naphtha (boiling at 137-l40 C.) 100Heat bodied linseed oil with drier so Naphtha (boiling at l95-2l0 C.) 40

This impregnating mixture was prepared as follows: 97.5 parts of rawalkali refined linseed oil was heated at 310 C. to a viscosity of T+8.5by the Gardner-Holdt scale. It was then cooled to 213 C. when 2.5 partsof solid lead-manganese resinate was added with stirring until theresinate was completely dissolved. The ratio of lead to to 1.50 parts ofmanganese.

'of a mat or sheet provided the'individual fibers manganese in theresinate was 6.42 parts of lead One hundred parts of asphalt (M. P. 170CT) "was heated to 246 C. and was then cooled to 211 C. when 100 partsof the lower boiling naphtha was added with stirring. As soon as theasphalt was entirely dissolved, parts of the '50%' solution of the heatbodied oil containing drier was added with stirring until a homogeneousmixture was obtained.

The impregnated sheet contained 48% saturant based on the total weightof product. It had a Mullen strength of 305 pounds, an Elmendorf tear of890 grams and a porosity of 1.4 seconds for 100 cc. displacement on theGurley Densometer. Itdid not stifien to a sufficient extent at -6 C. tocause cracking when bent quickly in a complete fold. There was nosurface exudation or stickiness when exposed to intense direct summersunlight for extended periods.

Valuable products are also obtained by using drying oil or asphalt aloneas the impregnating agent.

Example If The paper base of Example I was impregnated with a mixtureconsisting of:

Heat bodied linseed oil with drier 140 parts Naphtha (boiling at 137-140C.) 100 parts The completely oxidized product obtained after squeezingout the excess solution with rolls contained 54% saturant based on thetotal weight of product. This sheet had a Mullen strength of 290 pounds,an Elrnendorf tear of 920 grams, and a porosity of 1.5 seconds for 100cc. displacement on'the Gurley Densometer.

Example III The felt of Example Iwasimpregnated with a compositionconsisting of:

Blown asphalt (M. P. 180 c.) 50 parts Toluol 50 parts The Elmendorftearing strength was 1450 grams and the solids absorption based on thetotal weight of the product was 58%. Although the amount of asphaltabsorbed in the sheet. is unusually high the product was flexible anddid not have an asphalt-like appearance.

Our preferred method of impregnating the felt base consists in passingthe sheet from a roll through an impregnating tank, containing 40% to60% solutions or dispersions of the drying oil, at a speed-regulated togive thorough impregnation. The impregnated sheet is first passedbetween two knivesto scrape off excess dispersion and thence into aheated drying chamber. The

dried product, on emerging from the chamber.

may be wound into a roll immediately or it may be passed betweenembossing or calendaring rolls to smooth the surface.

In order to obtain the maximum increase'in freeness and crinkle by ourcaustic treatment, a,

have sufiicient freedom of movement and are not compacted or felted asin a finished sheet of paper. be formed on a Fourdrinier or cylindermachine from a. water suspension or from a caustic soda dispersion belowmercerizing activity and while the mat is still in a loose uncompactedcondition,

before heat drying, the caustic soda solution of mercerizing activitymay be applied to the surface of the sheet. The force of gravity willcarry the mercerizing solution through the sheet and For example, a matof untreated fibers may all of the fibers will be crinkled in situ,though i not to the samedegree as when they are dispersed in the form ofpulp. Or when still further crinkling is required, the fibers treated inpulp form may be dried as loose pulp, or as loose sheets, and thenredispersed to form sheets, thus adding still more bulk to the finishedsheet.

The caustic alkali may be replaced by solutions of other mercerizingreagents of equivalent activity as for instance solutions of zincchloride, ferric chloride hexahydrate, cuprammonium, calciumthiocyanate, sulfuric acid, etc.

Among pulps other than krait which may be used in the practice of thepresent invention are sulfite and soda jpulp, bleached or unbleached.Pulps from sources other than wood may also be used by first subjectingthe fibers to treatment which will reduce them to paper making length.Sheets made from pulps that have been bleached after the alkalitreatment are especially soft and porous.

In order to obtain various degrees of absorbency and strength in theimpregnating base, we may treatmixtures consisting of reactive fibersand fibers such as rope, which are less reactive to the treatmentdisclosed herein. Likewise, we may make the base material from variousmixtures of the treated or crinkled fibers with untreated fibers. Thetreated fibers should preferably constitute at least 23% of the mixture.

The absolute freeness values referred to herein are the values obtainedby using the special freeness tester described in our patent previouslyreferred to and are expressed as the time in seconds for the water levelof a dispersion of the pulp, at 25 C. containing 5 grams of bone drypulp in sufficient water to make 1000 cc. of .pulp suspension, to drop30 centimeters when the suspension is contained in a vertical glass tube1 13/16 inches in diameter closed at the bottom with a circular brasswire screen 1 inches in diameter, 0.006 inch thick and having a mesh of50 70.

Pulp such as treated in accordance with the present invention with asolution at the minimum strength within the mercerizing range, about 8%caustic soda at room temperature, is increased in freeness about 14%.The percent increase in freeness becomes rapidly greater as the causticconcentration rises to about 18%. Above this concentration a very slightadditional increase in freeness takes place until'the concentrationreaches about 24%, above which it is not desirable to go because theslight additional increase in crinkle doesnot justify the expense ofhigher caustic concentrations, and the wetting properties of thesolution become poorer, requiring at a 35% concentration a too largeexcess of the strong solution for complete wetting. The felts which givethe most outstanding results in the present process are those which havebeen -made with pulps treated with mercerizing soluabove 10.5% at 25 C.which causes an increase in freeness of from 35% to as high as 60%.

The absolute freeness values of the pulps used in the presentprocess areunusually high and serve to identify the pulp. The absolute freeness maybe as high as 15 seconds for a pulp having a freeness increase of 60%.In our process for producing improved impregnated fabric products thebest results are obtained with pulps having a freeness between 15 and 28seconds which corresponds to a freeness increase of 35% to 60% for pulpssuch as kraft pulp. Pulps of this freeness are obtainable by usingcaustic soda solutions of 10.5% to 18% concentration and above roomtemperature in accordance with the procedure outlined above. Pulpshaving a final ireeness of 20 to 40 seconds corresponding to a rreenessincrease of 15% to 35%, obtainable with 8% to 10.5% caustic soda at roomtemperature, also felt into products capable of absorbing largequantities of asphalt and drying oils.

The impregnated products of the above examples are still relativelyporous after impregnation, and coating films are therefore readilyanchored to them. This makes possible the production of artificialleather of a highly pleasing appearance which is very limp and flexibleand which at the same time is exceptionally strong.

The finishing coat for the impregnated products may be of the type knownto be useful in the manufacture of artificial leather products. Weusually prefer pigmented rubber and pyroxylin compositions such as thefollowing:

Example I V Parts Pyroxylin 1.00 Castor oil 1.90 Pigment 0.60 Ethylalcohol (denatured) 5.00 Ethyl acetate 4.50 Butyl acetate 0.50

Example V Parts Rubber (smoked sheet) 57.50 Zinc oxide 30.00 Litharge8.50 Lamp black 3.00 Sulphur 0.75 Palm oil 0.25 Naphtha 200.00

when a sizing coat is desired for securing good anchorage, the followingcomposition is suitable:

Parts Pyroxylin 4.00 Orange shellac 4.00 Ethyl alcohol (denatured) 25.00Ethyl acetate 22.50 Butyl acetate 2.50

Our improved artificial leather and impregnated products in general maybe identified by separating the base from the impregnating and coatingmaterials with suitable solvents and noting the freeness of the pulp ofthe base and its response to the test for mercerizecl fibers. If thepulp has been crinkled with caustic soda of mercerizing strength thefibers are not only changed as viewed through the microscope, from theribbon-like to rod-like form, but they also respond to the test withzinc chloriodine which distinguishes pulps or papers treated with sodiumhydroxide solutions of mercerizing activity. While pulps treated withthis strength of caustic for periods longer than those whichcharacterize g essee? the present invention also respond to the zincchloriodine test, they are dliferentiated by their freeness, since theyseldom have a ireeness as determined by the method described hereinfaster than 60 scconds. Pulps that have been manufactored by the sodaprocess in which wood chips are cooked with 8% to 11% of sodiumhydroxide at high temperature and pressure show only a slight colorationeasily distinguished from that obtained when this pulp is furthertreated with caustic as described herein.

The prompt occurrence of blue color indicates that the pulp has beentreated with about 8% to 35% sodium hydroxide. H the color is very deep,it indicates that the concentration of the solution (at roomtemperature) was above 13% and graduations of lighter shades indicateconcentrations down to the point where mercerizing activity begins.Mixtures of treated and untreated fibers are recognized under themicroscope after staining with zinc chloride solution. The 'colorpersists several days with bleached sulfite pulps treated by the presentprocess. Unbleached kraft pulps treated likewise give a color almostblack due to the brown color of the pulp and it fades within a fewhours.

In the practice of our invention, any ofthe fatty oils of a dryingnature, such as blown, heat bodied or raw China wood oil; fish oil andsoya bean oil, may be used, either alone or in con junction withasphalt. Pigments in various amounts may be added to the drying oilbefore saturation in order to give color or hardness.

The asphalts suitable in producing our improved impregnated productsinclude the blown asphalts, steam refined asphalts, and stearin pitches.The asphalt used may be in the form of an organic or aqueous dispersionor the felt base may be impregnated with the melted asphalt. Althoughasphaltic materials such as asphalts and pitches have been cited hereinspecifically, other bituminous materials having satisfactory meltingranges and adhesive properties are applicable to the purposes of thepresent invention.

The residual porosity which enables our impregnated products to takefinishing coats is a valuable feature of our invention. The prior artmaterials which have sufiicient residual porosity for the anchorage oftop coatings are usually deficient in tearing strength. Known high alphacellulose base material is not only too expensive for the purposes ofthe present invention, but the impregnated products seldom possesssatisfactory residual porosity except when the solids content is low andcertain impregnating media are used.

By means of the present invention, we obtain highly advantageous resultswithout resorting to the usual processes of making highly purified pulpwith attendant costs and further defibering into finer fibers.

Asphalt is valuable as an impregnating agent for our felt because of itspermanence and water resistance. However, asphalt does not produce suchresilient impregnated products as the drying=oi1 compositions, so it isdesirable to utilize the properties of both drying oils and asphalts.When drying oils are prepared by heat bodying or by combination of heatbodying and blowing, they are miscible with asphalts such as those citedherein and they form saturating compositions that are of more value thancompositions from. either the drying oil or asphalt alone. Theseadvantages are mainly that the temperature is lowered at which theimpregnated felt becomes stifi enough to crack on bending, theimpregnated sheet is drier on the surface at high temperatures ofservice such as the temperature obtained on an oxidized linseed oilprevents the asphalt from flowing evenwhen heated above the meltingpoint of the asphalt.

Our products obtained by impregnation with drying oil are particularlyvaluable inasmuch as they possess the combination of properties .mostdesired for the purposes of the present invention and not completelyobtained with other impregnating media. Our drying oil impregnatedprodnot is a tough material resistant to abrasion, re-z silient, waterproof, and non-plastic and contrasts markedly with the dense appearingdrying oil impregnated paper heretofore produced which have a low tearresistance and are susceptible to cracking at moderately lowtemperature. The blown drying oil impregnated products described hereinretain their resilience and freedom from creasing for a great manyyears. They have unusual aging properties and we have found them to bejust as pliable after five years as when first prepared. They also havethe advantage of low cost, ease in compounding and low solventrequirements for making compositions low enough in fluidity forimpregnation.

Our impregnated products have the saturant uniformly distributedthroughout the sheet. This makes possible the production of extremelyflexible products because the impregnating medium is not concentrated atthe surface of the sheet due to the filtering effect of conventionalabsorbent papers on colloidal particles. The artificial leather productshave the finishing coat firmly'anchored because of the high residualporosity of the impregnated sheet. The product may contain large ratiosof water resistant materials, such as asphalts, and yet retain felt-likecharacteristics. The impregnating material is distributed uniformlythroughout the sheet and does not have an un-impregnated core because ofthe straining or filtering of the impregnating media at the surface ofthe sheet or because of a denser formation in the center of the sheetOur products are usefulnot only as decorative limp artificial leatherfor book binding, etc., but are also particularly useful in shoe partsbecause the breathing properties (residual porosity) are comparable toleather; Our products are also usefi'l for gasket materials, floorcoverings, electrical insulation, wall coverings, and roofing materials.

As many apparently widely different embodiments of this invention may bemade Without departing from the spirit and scope thereof, it

is to be understood that we do not limit ourselves to the specificembodiments thereof except as defined in the appended claims.

We claim:

1. As an article of manufacture, a sheet of felted artificially crinkledcellulose fibers impregnated with a mixture of drying oil and bituminousmaterial, said fibers having a freeness of 15 to 40 seconds and havingthe substantially circular form in cross section which characterizescellulose fibers treated with solutions of mercerizing activity. a

2. As an article of manufacture, a sheet of felted artificially crinkledcellulose fibers impregnated with a mixture of drying oil and bituminousmaterial, said fibers having a freeness of 15 to 28 seconds and havingthe substantially circular form in cross section which characterizescellulose fibers treated with solutions of mercerizing activity.

3. The article set forth in claim 1 wherein the bituminous material isasphalt.

4. The article set forth in claim 2 wherein the bituminous material isasphalt.

5. As an article of manufacture, a sheet of artificially crinkled papermaking fibers impregnated with drying oil, said fibers having a freenessof 15 to 40 seconds and having the substantially circular form in crosssection which characterizes cellulose fibers treated with solutions ofmercerizing activity.

6. As an article of manufacture, a sheet of artificially crinkled papermaking fibers impregnated with drying .oil, said fibers having afreeness of 15 to 28 seconds and having the substantially circular formin cross section which characterizes cellulose fibers treated withsolutions of mercerizing activity.

'7. As an article of manufacture, a sheet of artificially crinkled papermaking fibers impregnated with drying oil, said fibers having a freenessof 15 to 40 seconds and exhibiting a blue stain when treated with zincchloriodine solution.

8. As an article of manufacture, a sheet of artificially crinkled papermaking fibers impregnated with drying. oil, said fibers having afreeness of 15' to 28 seconds and exhibiting a blue stain when treatedwith zinc chlorodine solution.

9. As an article of manufacture, a sheet of artificially crinkled papermaking fibers impregnated with bituminous material, said fibers having afreeness of 15 to 40 seconds and having the substantially circular formin cross section which characterizes cellulose fibers treated withsolutions of mercerizing activity.

10. As an article of manufacture, a sheet of artificially crinkled papermaking fibers impregnated with bituminous material, said fibers having afreeness of 15 to 28 seconds and having the substantially circular formin cross section which characterizes cellulose fibers treated withsolutions of mercerizing activity.

11. As an article of manufacture, a sheet of artificially crinkled papermaking fibers impregnated with bituminous material, said fibers having afreeness of 15 to 4.0 seconds and exhibiting a blue stain when treatedwith zinc chloriodine solution.

12. As an article of manufacture, a sheet of artificially crinkled papermaking fibers impregnated with bituminous material, said fibershavduced, and impregnating the sheet' with a mix- I ture of drying oiland bituminous material.

15. A process of manufacturing impregnated products which comprisesdispersing paper pulp with a solution of mercerizing activity, stoppingthe reaction before it proceeds substantially beyond a superficialmercerization of the fibers, depositing a sheet of the crinkled fibersthus produced, and impregnating the sheet with drying oil.

16. A process of manufacturing impregnated products which comprisesdispersing paper pulp with a-solution of mercerizing activity, stoppingthe reaction before it proceeds substantially beyond a. superficialmercerizationof the fibers,

depositing a sheet of the crinkled fibers thus' produced, andimpregnating the sheet with bituminous material.

17. The process set forth in claim 14 in which said solution has amercerizing activity equivalent to that of an aqueous sodium hydroxidesolution between 10.5 and 35% concentration.

18. The process set forth in'claim 15 in which said solution has amercerizing activity equivalent to that of an aqueous sodium hydroxidesolution between 10.5 and 35% concentration.

19. The process set forth in claim 16' in which said solution has amercerizing activity equivalent to that of an aqueous sodium hydroxideso lution between 10.5 and 35% concentration.

FRANK H. MCCORMICK. GEORGE L. SCHWARTZ.

